• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 275 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

AFE4490SPO2EVM: Calculating %SpO2 and Setting Calibration Current

AFE4490SPO2EVM: Averaging

Alyssa Everson
Prodigy 30 points
Part Number: AFE4490SPO2EVM
Other Parts Discussed in Thread: AFE4490

Hello,

I have a question regarding the averaging mechanism of the AFE4490.

I see that the maximum number of averages is 16 and that the equation for averages is given by: (0.25 * PRP / 50us) -1.

This makes sense to me if the duty cycle is 25%. However, if the duty cycle is less than 25%, should the 0.25 in the equation above be changed to the value of the new duty cycle?

The GUI allows me to set the number of averages given by the equation, even if it should be too many averages given the shorter duty cycle. Does this mean that the "extra" averages are insignificant?

Say a 5% duty cycle should correspond to 4 averages max, if I use 0.05 rather than 0.25 in the equation. If I set the number of averages to 16 anyway, are the extra 12 averages essentially ignored because the LED is only being sampled for ~200 microseconds? Or should including the full 16 averages improve my signal?

Thanks!

  • 0
    TI__Prodigy 215 points

    Hi,

      The NUMAV parameter is applicable in the CONV phase since the ADC operates in the CONV phase. The LED ON duty cycle does not impact the calculation of the max value of the NUMAV parameter. You just need to set the CONV phase width long enough to allow enough time for the ADC to convert sufficient number of times and average the conversions.

    Having said this, a NUMAV of 4 might be sufficient to get the benefit of ADC averaging. The operation of averaging the ADC conversions only suppresses the ADC contribution to the overall noise. Also the effect of NUMAV on the overall noise gets less significant at higher TIA gain settings.

    Regards,

    Anand.